Decibel And HDMI audio

Discuss Decibel, a high quality audio player.
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maxdb
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Decibel And HDMI audio

Post by maxdb » Fri May 25, 2012 6:27 pm

For high quality music listening I use a USB DAC with Decibel, but for a change or just for fun, I would like to use HDMI audio out to a 7.1 channel-capable surround sound processor. The problem is... the surround processor identifies itself as an 8-channel device so the Mac (an aluminum unibody Mini running Snow Leopard 10.6.8 with no likelihood of changing to Lion any time soon) sends 8-Channel PCM. When the surround processor thinks is receiving 8 audio channels, it doesn't offer any processing choices ike Pro Logic IIx Music mode or Neo:6 Music mode.

Is there any way to get stereo music played by Decibel to force the Mac to send what the surround processor thinks is 2-channel PCM over HDMI so music modes like PLIIx and Neo:6 are available on the surround processor? When you send 8-channel PCM to the surround processor, no surround processing modes are available at all (nor would you expect them to be available).

Clicking Stereo mode in Audio MIdi does nothing, even if the Mac is rebooted and it comes up in Stereo mode (Speaker Configuration) the surround processor still sees 8-channel PCM from the Mac... even though 6 channels carry no music data. And, of course, the surround processor offers no way to manually treat the HDMI input from the Mac as 2-channel PCM.

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sbooth
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Re: Decibel And HDMI audio

Post by sbooth » Sun May 27, 2012 12:28 pm

I was going to suggest tweaking Audio MIDI Setup with a custom channel map, but it sounds like you've already tried it. Does the surround processor support stereo input (from the Mac's perspective) or is it always 8 channels?

maxdb
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Re: Decibel And HDMI audio

Post by maxdb » Sun May 27, 2012 6:26 pm

The processor does detect stereo HDMI inputs from other sources, like the DirecTV box... if a program happens to be in stereo (rather than DD 5.1 common for HD channels), the processor allows choosing PLIIX or Neo:6 modes. The issue seems to be not being able to get the Mac (Mini) into stereo mode. If I pick one of the 2-channel stereo options in Audio Midi, it immediately jumps back to 8-channel 24-bits after the drop-down goes away. So even though other modes appear in the drop-down list, I can't change from 8-channel mode. If I could get the Mac into 2-channel mode, I'm sure the surround modes in the processor would work just fine. But there seems to be something about the way the Mac handles EDID info that if the source says it is capable of 8-channels and 24-bits, that's all the Mac will ever send, even if it is only working with a 2-channel PCM source. Unless there's some setting or control somewhere that is not intuitively obvious to the casual observer.

maxdb
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Re: Decibel And HDMI audio

Post by maxdb » Mon May 28, 2012 4:36 am

Re-reading the previous post, it might not be clear what I was trying to describe...

The DirecTV box changes audio formats (over HDMI) with some regularity... for example, when viewing an HD channel, it's common to have commercials switch to 2-channels... the processor "sees" those changes and the DirecTV box transitions between the number of active channels seamlessly. I don't have to do anything. When the DirecTV box sends 5.1, the processor decodes it and sends 5.1 sound to the speaker system (currently 5.1 but is sometimes 7.1). When the DirecTV box sends stereo over HDMI, the processor "sees" the change and presents a wide range of surround modes to choose from (no options when you have a 5.1 system with 5.1 program, you just get the DD decoded).

The Mac, on the other hand, ALWAYS sends 8-channel PCM no matter how many channels are in the source. That means if I send stereo over HDMI, the processor still sees 8-channels of PCM. If I send 4.0 (a Quad mix) or 5.1, the processor still sees 8-channel PCM. There's nothing in the Mac that changes the number of active channels as far as I can tell. Seems a rather odd omission.

I'm not sure whether Decibel is locking-in the 8-channel PCM output or whether the Mac is doing it... I haven't got any other playback software that handles more than stereo playback (have not tried iTunes I don't use it for anything).

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sbooth
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Re: Decibel And HDMI audio

Post by sbooth » Tue May 29, 2012 10:55 am

Do you have HALLab available? I'd be curious to see what formats it says your device supports. It's part of Apple's audio tools and you can download it from https://developer.apple.com/downloads/i ... 0Xcode%20-

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